# FIND_PACKAGE(HELLO)
# FIND_PACKAGE(HELLO QUITE)
# QUITE 变量就会体现到 HELLO_FIND_QUIETLY 变量中
FIND_PACKAGE(HELLO REQUIRED)
# REQUIRED 会体现到 HELLO_FIND_REQUIRED 变量中

IF(HELLO_FOUND)
    ADD_EXECUTABLE(main main.cpp)
    INCLUDE_DIRECTORIES(${HELLO_INCLUDE_DIR})
    TARGET_LINK_LIBRARIES(main ${HELLO_LIBRARY})
ENDIF(HELLO_FOUND)